Individuals with autism spectrum disorder (ASD) experience profound difficulty in social interactions. Problems maintaining eye contact, or shared gaze, emerge early in life and persist throughout development. The social challenges experienced by people with ASD are most evident in dynamic, interactive contexts~ however, most brain research in ASD has studied neural responses to social information in less realistic contexts, such as passively viewing static faces on a computer monitor. In the curren study, we propose to combine high-speed eye-tracking (ET~ to measure where a person looks on a computer screen) and electroencephalographic recording (EEG~ to measure brain response). Integration of these methods enables simulation of social interactions y animating on-screen faces that respond to the participant's eye gaze. In this way, we study interactions that, as in real life, are controlled by eye contact rather than a keyboard or computer device. We use computer-generated, highly realistic faces that respond to the gaze of participants by looking back or making a facial expression. In three experiments, we will examine patterns of visual attention and associated brain response in ASD and typically developing counterparts while viewing (a) static faces, (b) interactive faces that respond to the viewer's gaze with reciprocated or averted eye contact, and (c) interactive faces hat respond to the viewer's gaze with a facial expression, such as a smile. This project will also collect information about social and communicative behavior to examine the relationship between neural response to shared gaze and social function. Preliminary data demonstrate the viability of this innovative approach and reveal a novel EEG marker for reciprocal eye contact that is attenuated in ASD and related to social performance. Our innovative approach will advance understanding of the brain bases of ASD by studying social perception in a naturalistic, interactive context. This research is a critical first step with significant clinial translational benefits, including identifying therapeutic targets, developing biologically-baed predictors of treatment response, creating new treatment approaches, defining subgroups of individuals with ASD, and detecting atypical brain development in ASD before behavioral symptoms become evident.